With the continuous development of electronic apparatuses towards super micromation, as well as the development of new computer, microelectronics, optoelectronics and communication theory and technology, the new wearable computing model of the concept that computing should fit human and contribute to the combination between human and machine has become possible. Wearable computing applications emerge in fields of military, industrial, medical, education, consumption and so on. In a typical wearable computing system architecture, the head-mounted display apparatus is a key component, which directs video image light emitted by the miniature image display apparatus (e.g. transmissive or reflective liquid crystal display, organic electroluminescent apparatuses, DMD apparatuses) to the user's pupil via the optical technology, and forms virtual and magnifying images in the near eye range and provides the user with intuitive and visual image, video and text information. The eyepiece optical system is the core of the head-mounted display apparatus, which can display virtual and magnifying images of micro images in front of the user's eyes.
The head-mounted display apparatus of compact size, light weight, convenient wearing and lighten load and so on is the development trend. Meanwhile, a large field-of-view angle determining the highly immersive visual experience and a comfort degree of the visual experience determined by the high image quality and low distortion, have constituted the key factors for evaluating the quality of the head-mounted display apparatus. In order to satisfy these requirements, the eyepiece optical system should meet the indices of the large field-of-view angle, high image resolution, low distortion, small field curvature, small volume and so on as far as possible, while meeting the above optical performances at the same time is a great challenge for the system design and aberration optimization.
The common eyepiece optical system is formed by a three-coaxial-lens assembly constituted by a first lens having a positive focus, a second lens having a negative focus and a third lens having a positive focus. Many prior documents have provided their own designs based on such structure. Patent literatures, such as reference document 1 (Publication No. CN101887166B), reference document 2 (Publication No. CN103217782A), reference document 3 (Publication No. CN104730706A), reference document 4 (Publication No. CN103988111A), reference document 5 (Publication No. CN104685402A), reference document 6 (Publication No. CN104603669A), reference document 7 (Publication No. U.S. Pat. No. 7,978,417B2), reference document 8 (Publication No. U.S. Pat. No. 8,345,139B2), have respectively provided eyepiece optical systems formed by three coaxial lenses having a positive focus, a negative focus and a positive focus, which eyepiece optical systems have low distortion (<3%) and high image quality. But these eyepiece optical systems have small effective viewing angles ranging from 16˜37 degrees, respectively, and fail to obtain a large field-of-view angle effect.
Reference document 9 (Publication No. U.S. Pat. No. 5,815,317A) has provided a head-mounted display apparatus composed of a singlet positive lens, a cemented doublet negative lens and a singlet positive lens, which can be considered as a positive-negative-positive structure as a whole capable of realizing a large field-of-view angle effect (>50 degrees). But this head-mounted display apparatus has too large aberration residua, such as the field curvature and astigmatism, and too poor image quality at the field edges to achieve high resolution optical effect, so that it is not conducive to long-time and comfortable visual experience.
As another three-coaxial-lens assembly, the positive-positive-negative optical structure having a large field-of-view angle can be applied for the eyepiece optical system. Reference document 10 (Publication No. CN104635333A) has provided an eyepiece optical system adopting the positive-positive-negative optical structure, which is capable of realizing a large field-of-view angle effect (>50 degrees). But meanwhile, such eyepiece optical system has a large off-axis aberration, together with a large residual chromatism, which reduces the optical resolution of the off-axis field and is not good for comfortable visual experience.
Reference document 11 (Publication No. CN104536130A) has provided an eyepiece optical system of positive-positive-negative-positive optical structure having a fourth lens with a positive focal power in additional to the positive-positive-negative three-coaxial-lens optical structure. Reference document 12 (Publication No. U.S. Pat. No. 5,877,900A) has provided an eyepiece optical system, in which a singlet positive lens, a singlet positive lens, a cemented doublet negative lens and a singlet positive lens are arranged coaxially and successively along the optical axis direction from the eye viewing side to the miniature image display apparatus side, and form a positive-positive-negative-positive optical structure as a whole. Although the eyepiece optical systems mentioned in both reference documents are capable of realizing a large field-of-view angle effect (>50 degrees) and meanwhile have a better off-axis aberration, system chromatism, and other optical indices, however, there are still residual aberration, such as the field curvature and astigmatism, which would result in significant difference of the image qualities in the central field and edge field. The closer to the edge, the lower the field optical resolution. No optical effect of high resolution in the full frame range is obtained.
Reference document 13 (Publication No. CN104570323A) has provided an eyepiece optical system, in which a singlet positive lens, a singlet positive lens, a singlet negative lens and a singlet negative lens are arranged coaxially and successively along the optical axis direction from the eye viewing side to the miniature image display apparatus side, and form a positive-positive-negative-negative optical structure. The eyepiece optical system has a large field-of-view angle effect (>70 degrees), while together with a too large distortion (>25%) which results in serious distortion of image display.
Reference document 14 (Publication No. US2014/0218806A1) has provided an eyepiece optical system for head-mounted display, in which a positive lens group constituted by two or three positive lenses and a negative lens group constituted by a cemented doublet lens of a biconcave lens and a biconvex lens or constituted by the cemented doublet lens of a biconcave lens and a biconvex lens and a singlet positive meniscus lens, are arranged coaxially and successively along the optical axis direction from the eye viewing side to the miniature image display apparatus side. The basic structure of the head-mounted display apparatus can be considered as a positive-positive-negative (cemented doublet lens) optical structure. Furthermore, a positive-positive-positive-negative (cemented doublet lens) optical structure is adopted in a preferable embodiment. The eyepiece optical system can obtain a large field-of-view angle effect (>50 degrees) and correct the residual aberration of the optical system. However, there are too many lenses which increase the product size and weight and make it uncomfortable for wearing. Moreover, the surface shape of the lens is too complicated to be produced in massive.
Reference document 15 (Publication No. CN101609208B) has also provided an eyepiece optical system for head-mounted display, in which a singlet positive lens, a singlet positive lens, a cemented doublet negative lens, a singlet positive lens and a singlet lens are arranged coaxially and successively along the optical axis direction from the eye viewing side to the miniature image display apparatus side to form a relatively complicated optical structure, which is capable of realizing a large field-of-view angle effect (>50 degrees). However, the above eyepiece optical systems all have large astigmatisms, and meanwhile when a plurality of lenses (more than 5 lenses) are applied to form an optical system, the product size and weight become too large for comfortable wearing experience.
Reference document 16 (Publication No. CN104965306A) has also provided an eyepiece optical system with a large field-of-view angle, in which a first lens, a second lens, a third lens and a fourth lens are arranged coaxially and successively along the optical axis direction from the eye viewing side to the miniature image display apparatus side to form a relatively complicated optical structure. Although such eyepiece optical system is capable of realizing a large field-of-view angle effect (>75 degrees), however, its image quality declines at the field edges when comparing with that at the field center, so the image quality is not uniform enough in the full frame. At the same time, optical materials having a large refractive index should be employed, which results in manufacturing cost and weight increase and increases manufacture difficulties.